mail = 'heythere'
'e' in mail

it prints ,

True because there is ‘e’ in the word ‘heythere’.

mail = 'heythere'
if 's' in mail:
    print('found it!')
else:
    print ('did not found it :(')

and it prints,

did not found it :(

list = [1, 4, 6, 8, 10]
8 in list

prints,

>>>True

15 in list

prints

>>>False

20 not in list

prints,

>>>True